Design and fabrication of a MEMS magnetic sensor utilizing ferromagnetic-piezoelectric composites

A high-sensitivity and self-biased MEMS magnetic sensor based on ferromagnetic-piezoelectric composites has been fabricated and characterized. Series of MEMS processes including silicon-quartz lower temperature eutectic bonding, quartz wafer thinning, electroplating of thick nickel thin films, etc., have been successfully demonstrated in creation of a quartz-nickel cantilever structure. Moreover, by laminating an additional metglas thin film, a zero-bias magnetic-electric coupling that arises due to magnetization grading at the interface of Ni-metglas has been observed. With the optimized structure, a magneto-electric voltage coefficient up to 60 V/cm·Oe has been demonstrated. With a measured low magnetic noise of 18 pT/Hz^1/2, a ~36 pT resolution and high converted sensitivity of 0.5 mV/pT are obtained at the mechanical resonant frequency of 122 Hz with zero dc biasing magnetic field. The targeted MEMS magnetic sensor has great potential applications in emerging biomagnetic imaging technologies such as magnetocardiography.